Toggle-switch-like crossover between two types of isolated skyrmions within the conical phase of cubic helimagnets

Leonov, A. O.; Bogdanov, A. N.; Inoue, Katsuya

doi:10.1103/physrevb.98.060411

Cited by 17 publications

(23 citation statements)

References 82 publications

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“…One expects that when h becomes higher than this field, metastable spirals rupture forming pairs of merons, each with a topological charge 1/2. 52,53 Merons, which may also nucleate at the boundary between the metastable spiral and conical domains, ultimately evolve into skyrmions at higher magnetic fields. Since the SkL phase remains metastable below the dashed line, one expects skyrmionic states to persist for fields lower than h = 0.11, until they undergo an elliptical instability into spiral states, 54 which explains the hysteresis effect shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

Multiple low-temperature skyrmionic states in a bulk chiral magnet

et al. 2019

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Magnetic skyrmions are topologically protected nanoscale spin textures with particle-like properties. In bulk cubic helimagnets, they appear under applied magnetic fields and condense spontaneously into a lattice in a narrow region of the phase diagram just below the magnetic ordering temperature, the so-called A-phase. Theory, however, predicts skyrmions to be locally stable in a wide range of magnetic fields and temperatures. Our neutron diffraction measurements reveal the formation of skyrmion states in large areas of the magnetic phase diagram, from the lowest temperatures up to the A-phase. We show that nascent and disappearing spiral states near critical lines catalyze topological charge changing processes, leading to the formation and destruction of skyrmionic states at low temperatures, which are thermodynamically stable or metastable depending on the orientation and strength of the magnetic field. Skyrmions are surprisingly resilient to high magnetic fields: the memory of skyrmion lattice states persists in the field polarized state, even when the skyrmion lattice signal has disappeared. These findings highlight the paramount role of magnetic anisotropies in stabilizing skyrmionic states and open up new routes for manipulating these quasi-particles towards energy-efficient spintronics applications.

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Section: Discussionmentioning

confidence: 99%

Multiple low-temperature skyrmionic states in a bulk chiral magnet

et al. 2019

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“…6(b)]. Contributions of more exotic three-dimensional spin textures, such as stacked spirals [52], chiral bobbers [53][54][55], quasimonopoles [56], and in-plane skyrmion tubes [46,57,58], to the scattering patterns are another possible explanation of this result. Further real-space investigations of the possible three-dimensional states using cryogenic coherent [36,59] or focused [46] soft-x-ray methods will help to clarify this question.…”

Section: Micromagnetic Simulation Of the Skyrmion Lattice In The Imentioning

confidence: 97%

Metastable solitonic states in the strained itinerant helimagnet FeGe

et al. 2020

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Tensile strain is a promising tool for the creation and manipulation of magnetic solitonic textures in chiral helimagnets via tunable control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Here, by using in situ resonant small-angle x-ray scattering, we demonstrate that skyrmion and chiral soliton lattices can be achieved as metastable states in FeGe lamella as distinct states under tensile strain and magnetic fields in various orientations with respect to the deformation. The small-angle scattering data can be well accounted for in the framework of the analytical model for a soliton lattice. By using the experimental results and analytical theory, the unwinding of metastable skyrmions in a perpendicular magnetic field as shown by a small-angle scattering experiment was analyzed via micromagnetic simulation.

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“…These symmetries are exempt from such an ordeal to look for stabilization mechanisms of metastable SkLs. In these materials at the field H c1 , thermodynamically stable spiral states give rise to the thermodynamically stable SkL via formation of merons representing ruptures of a spiral state each with the topological charge Q = 1/2 [35,36]. Moreover, Néel (C nv ) and antiskyrmions (D 2d ) are not modified by additional surface twists along z [30]; that is, their physics remains the same in both bulk and nanofabricated magnets.…”

Section: B Stability Of Skyrmions In Helimagnets With and Without Thmentioning

confidence: 99%

“…An applied magnetic field, h||[001], induces the conical state, where the state with the helical propagation vector along the magnetic field corresponds to the global energetic minimum, whereas the helices along the other directions become metastable solutions. Such metastable spiral domains, however, may give rise to the thermodynamically stable skyrmions [24,35,36], which therefore form clusters within the conical state. These would be nonaxisymmetric skyrmions similar to those that were recently introduced theoretically in Refs.…”

Section: A Skyrmion Clusters As Initiators Of Fopt From the Conical mentioning

confidence: 99%

Skyrmion clusters and conical droplets in bulk helimagnets with cubic anisotropy

Leonov

Pappas

2019

Phys. Rev. B

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Recent experimental findings in the bulk cubic helimagnet and Mott insulator Cu 2 OSeO 3 highlight the paramount role of cubic anisotropy in stabilizing novel chiral and skyrmion phases. It was indeed found that if a magnetic field is applied along the easy 001 crystallographic direction, competing cubic and exchange anisotropies tilt the wave vector of the conical spiral away from the magnetic field [Qian et al., Sci. Adv. 4, eaat7323 (2018)]. Furthermore, in this configuration skyrmions have been observed in a broad range of temperatures and magnetic fields [Chacon et al., Nat. Phys. 14, 936 (2018)]. Starting from these experimental observations and on the basis of a phenomenological Dzyaloshinskii theory, we investigate additional implications of the cubic anisotropy for this specified field direction. By including cubic anisotropy we show that the phase transition between the conical and field-polarized or homogeneous states becomes first order. Furthermore, we show that this transition is accompanied by the formation of conical droplets-domains of the conical phase in the homogeneous state. We investigate the internal structure of these droplets, which at their boundaries encompass alternating regions of positive and negative energy densities with respect to the homogeneous state. We thus deduce that these droplets may be zipped and unzipped in phase during the first-order phase transition that occurs by either increasing or decreasing the magnetic field. On the other hand, we show that in the conical phase skyrmions may form clusters due to their attractive mutual interaction. However, in the homogeneous state, the skyrmion-skyrmion interaction becomes repulsive, and the skyrmion clusters expand and disperse isolated skyrmions. This mutual skyrmion repulsion prevents the stabilization of skyrmion clusters even if the energy of isolated skyrmions is lower than that of the homogeneous state. Yet this skyrmion dispersal may be prevented if skyrmions are surrounded by the circular spiral state and form skyrmion bags. Such a scenario could explain the existence of skyrmions in the field-polarized state reported experimentally.

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Toggle-switch-like crossover between two types of isolated skyrmions within the conical phase of cubic helimagnets

Cited by 17 publications

References 82 publications

Multiple low-temperature skyrmionic states in a bulk chiral magnet

Multiple low-temperature skyrmionic states in a bulk chiral magnet

Metastable solitonic states in the strained itinerant helimagnet FeGe

Skyrmion clusters and conical droplets in bulk helimagnets with cubic anisotropy

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